Scientists from ExxonMobil and the US-based Georgia Institute of Technology have developed a new process that could significantly cut the amount of energy and emissions associated with plastics manufacturing. The process uses a molecular-level filter in a form of reverse osmosis to separate PX, which is used to make PET, from complex hydrocarbon mixtures. Existing commercial-scale processes rely on energy and heat to separate the molecules.

“In effect, we’d be using a filter with microscopic holes to do what an enormous amount of heat and energy currently do in a chemical process similar to that found in oil refining,” said Mike Kerby, ExxonMobil’s corporate strategic research manager. The research has shown that PX can be separated from other aromatics by pressing them through a membrane that acts as a high-tech sieve. ExxonMobil said the amount of energy used worldwide in conventional aromatics separation processes, such as crystallization or adsorption with distillation, is equivalent to about 20 average-sized power plants.

The carbon-based membrane is said to be about 50 times more energy efficient that current membrane separation technology. Because the new membrane is made from a commercially available polymer, ExxonMobil believes it has potential for commercialization and integration into industrial chemical separation processes. The organic solvent-based route is also believed to be the first use of reverse osmosis with carbon membranes to separate liquid hydrocarbons.

“By applying pressure at room temperature, the membrane is able to concentrate PX from a mixture at high rates and low energy consumption relative to state-of-the-art membranes. This mixture could then be fed into a conventional thermal process for finishing, which would dramatically reduce total energy input,” explained Ryan Lively, lead researcher and an assistant professor at Georgia Tech.

However, the technology still faces challenges. The membranes need to be tested under more severe conditions as industrial mixtures often contain multiple organic compounds and may include materials that can foul membrane systems. The researchers must also learn to make the material consistently and demonstrate that it can withstand long-term industrial use.

“Our next steps are to further the fundamental understanding in the lab to help develop a plan for pilot plant-scale demonstration and, if successful, proceed to larger scale,” said Benjamin McCool, advanced research associate at ExxonMobil, and co-author of the research. If brought to industrial scale, the technology breakthrough could cut industry’s global CO₂ emissions by up to 45 million t/y, equivalent to roughly five million US homes. It could also cut the energy costs related to global plastics production by up to $2 billion a year.

According to ExxonMobil, chemical plants account for about 8% of global energy demand, and about 15% of the projected growth in demand to 2040. Results of the research have been published in the peer-reviewed journal Science.